1. Field of the Invention
The present invention relates to a mobile communication system provided in a mobile body, for communicating via a communication network so as to transfer data. More particularly, the present invention relates to a mobile communication system capable of enhancing flexibility in a layout of the communication network and improving reliability.
2. Description of the Related Art
In recent years, there is a remarkable progress in higher functioning and computerization of the mobile body such as a car, an airplane, a train and a vessel. According to the higher functioning and the computerization, numbers of sensors, in-vehicle equipments, signal lines (e.g., wire harnesses) for connecting the sensors and the in-vehicle equipments, and the like, which are installed in the mobile body, are steadily increasing.
Therefore, for the purpose of achieving the reduction in weight of the wire harnesses and also sharing the vehicle information, an introduction of an in-vehicle network having high-speed and large-capacity is being promoted.
FIG. 3 is a view showing a configuration of a mobile communication system of the related art (for example, refer to JP-A-2002-175597). In this case, explanation will be made with the car as an example of the mobile body. In FIG. 3, a vehicle total-control device 11 issues the instructions to various control units respectively by using information from sensors so as to execute the control of the vehicle entirely. An image processing camera 12 and a radar 13 are sensors for recognizing a driving environment. An engine control unit 14, a transmission control unit 15, a brake control unit 16, and a steering control unit 17 are control units respectively, and control various in-vehicle equipments (not shown) connected to the control units.
A wire harness 18 is a bus that connects the vehicle total-control device 11, the sensors 12, 13, and the control units 14 to 17 mutually respectively. Also, a wire harness 19 is a bus that connects the vehicle total-control device 11, the sensors 12, 13, and the control units 14 to 17 mutually respectively, as well as the wire harness 18. In this case, the wire harness 18 is a signal line that is normally used, and the wire harness 19 is a signal line for fail-safe that is used when the failure occurs in the wire harness 18.
An operation of such mobile communication system will be explained hereunder.
The vehicle total-control device 11 communicates with the sensors 12, 13 via the wire harness 18, and collects various information relating to the driving environment. In this case, the information may be collected from other sensors which are not shown (for example, a speed sensor, a tire pressure sensor, etc.). Then, the vehicle total-control device 11 communicates with control units 14 to 17 via the wire harness 18 respectively and issues the instructions based on the information from the sensors 12, 13. Then, control units 14 to 17 controls the in-vehicle equipments (not shown) in compliance with these instructions.
Also, when the vehicle total-control device 11 cannot perform communication since the failure occurs in the wire harness 18, the vehicle total-control device 11 performs communication using the wire harness 19 for fail-safe so as to transfer data.
Then, FIG. 4 is a view showing another configuration of the mobile communication system in the related art (for example, refer to Japanese Patent No. 2904296). FIG. 3 shows the bus connection type network in which all the devices (the vehicle total-control device 11, the sensors 12, 13, and control units 14 to 17) are connected to the wire harnesses 18, 19 in parallel. The devices having high relevancy may be grouped together based on the number of the sensors 12, 13 and the control units 14 to 17 and the purpose of application.
Here, in FIG. 4, the same reference symbols are affixed to the same portions as those in FIG. 3, and their explanation will be omitted herein. In FIG. 4, a gateway 20 is provided instead of the vehicle total-control device 11. A driving system network 100 is a network in which the devices related to driving are grouped together, and is provided with the sensors 12, 13, and the control units 14 to 17.
A car body system network 101 is a network in which devices related to the car body are grouped together, and is provided with a temperature sensor 21, an illuminance sensor 22, an air conditioner control unit 23, a lamp control unit 24, and a wiper control unit 25.
An information system network 102 is a network in which the devices related to music, image, etc. are grouped together, and is provided with an audio control unit 26, and a navigation control unit 27. In the respective networks 100 to 102, each units and sensors are connected mutually via the wire harnesses 18, 19. In this case, the sensors 12, 13, 21, 22, and the control units 14 to 17, 23 to 27 are nodes. Also, respective networks 100 to 102 are connected mutually with the gateway 20.
An operation of such system will be explained.
The gateway 20 receives data from the nodes 12 to 17, 21 to 27 in respective networks 100 to 102, and issues instructions to the control units 14 to 17, 23 to 27 based on the data. The control units 14 to 17, 23 to 27 respectively control the in-vehicle equipments in compliance with the instructions. In addition, the gateway 20 performs data transfer between the different networks (e.g., transfer data from the network 100 to the network 102).
In addition, when the communication cannot be performed since the failure occurs in the wire harness 18, the data transfer is executed by performing the communication using the wire harness 19 for fail-safe. For example, when the failure occurs in the wire harness 18 in the driving system network 100, the communication is performed via the wire harness 19 for fail-safe only in the driving system network 100.
Then, the wire harnesses 18, 19 shown in FIG. 3 and FIG. 4 will be explained. As the transmission speed becomes higher, a metal transmission by the wire harness radiates noise from a transmission line and is easily influenced by noise from an external path. Therefore, the measure to suppress the radiation of the noise and the influence of the noise must be taken. However, problems occur due to an increase in cost and an increase in weight. As a result, communication via an optical fiber, which is not influenced by the noise, attracts attention nowadays.
Furthermore, as shown in FIG. 4, with the increase of the in-vehicle networks, in some cases the data handled in the in-vehicle network are classified into the car body system network (lamp, wiper, etc.) 101, the driving system network (engine, brake, etc.) 100, the information system network (navigation, audio, etc.) 102, and the like, based on the purpose of application.
In the classification shown in FIG. 4, particularly as the standard of the information system network 102, IDB-1394 (ITS Data Bus-1394) that is widespread mainly in Japan and the United States of America, and MOST (Media Oriented Systems Transfer) that is widespread mainly in Europe are developed. Also, an introduction into the real car of the in-vehicle network employing the optical fiber instead of the metal transmission is started.
However, these standards are applied to the information system network 102. In the driving system network 100 and the car body system network 101, for the reason that a transmission capacity is small and the cost can be suppressed low, the metal transmission via the wire harnesses 18, 19 is still used as the in-vehicle network.
The mobile body is used in a poor environment in which the temperature changes drastically due to the outdoor temperature and the radiant heat from the in-vehicle equipments. Therefore, the mobile communication system is also used in the poor environment. Under such situation, in order to perform the communication with high reliability, measures such as dualizing the wire harnesses 18, 19 are adopted. Of course, such a problem exists that a cost required for the measure and a weight of the wire harnesses 18, 19 are increased.
Furthermore, in the bus connection type network as shown in FIG. 3, there exists a problem that flexibility in the layout is low. In addition, since all nodes 11 to 17 are affected when the wire harnesses 18, 19 in the transmission line are disconnected, such a problem exists that the reliability is low.
Also, in FIG. 4, the in-vehicle network is divided into a plurality of networks 100 to 102, and then integrated by connecting the buses of respective networks 100 to 102 via the gateway 20. As a result, the flexibility in the layout and the reliability are improved rather than those of FIG. 3.
However, there exists a problem that, since the bus connection type network is employed in the inside of the networks 100 to 102 respectively, both the flexibility in the layout and the reliability are low. In addition, there exists a problem that, since all the information gathers in the gateway 20, the high-speed bus line is required and thus the cost is increased. Further, the gateway 20 not only controls a data path in the in-vehicle network but also serves as the central control unit that is provided in the uppermost position. Therefore, for the gateway 20, there exists a problem that the needs for high performance and reliability become high, resources required for design and development must be concentrated, and the cost is increased.